The overall objective of the total project is to enumerate those factors relating to the persistence and recurrence of urinary tract infection. During the past year, our efforts have focused on virulence of K-antigen-containing strains of E. coli in experimental pyelonephritis. Although 22 strains which contained K antigen were more significantly associated with experimental infection than 9 strains with no antigen, these strains were no more commonly isolated from the upper urinary tract of patients. During the coming year, we plan to ascertain whether strains of E. coli which possess antigens cross-reactive with the capsular polysaccharides of other virulent organisms, i.e., Hemophilus influenzae type b, are more frequently isolated from patients with pyelonephritis as opposed to cystitis. In addition, we plan to study the virulence of these strains in experimental aniamls.